132 lines
2.7 KiB
Markdown
132 lines
2.7 KiB
Markdown
---
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title: Go Interfaces Considered Harmful
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date: 2018-12-03
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---
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# Go Interfaces Considered Harmful
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A group of blind men heard that a strange animal had been brought to the town function, but none of them were aware of its type.
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```
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package blindmen
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type Animal interface{}
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func Town(strangeAnimal Animal) {
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```
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Out of curiosity, they said: “We must inspect and know it by type switches and touch, of which we are capable”.
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```
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type Toucher interface {
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Touch() interface{}
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}
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```
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So, they sought it out, and when they found it they groped about it.
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```
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for man := range make([]struct{}, 6) {
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go grope(man, strangeAnimal.(Toucher).Touch())
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}
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```
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In the case of the first person, whose hand landed on the trunk, said “This being is like a thick snake”.
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```
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type Snaker interface {
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Snake()
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}
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func grope(id int, thing interface{}) {
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switch thing.(type) {
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case Trunker:
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log.Printf("man %d: this thing is like a thick snake", id)
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```
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For another one whose hand reached its ear, it seemed like a kind of fan.
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```
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type Fanner interface {
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Fan()
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}
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// in grope switch block
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case Fanner:
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log.Printf("man %d: this thing is like a kind of fan", id)
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```
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As for another person, whose hand was upon its leg, said, the it is a pillar like a tree-trunk.
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```
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type TreeTrunker interface {
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TreeTrunk()
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}
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// in grope switch block
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case TreeTrunker:
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log.Printf("man %d: this thing is like a tree trunk", id)
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```
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The blind man who placed his hand upon its side said, “it is a wall”.
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```
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type Waller interface {
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Wall()
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}
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// in grope switch block
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case Waller:
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log.Printf("man %d: this thing is like a wall", id)
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```
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Another who felt its tail, described it as a rope.
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```
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type Roper interface {
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Rope()
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}
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// in grope switch block
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case Roper:
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log.Printf("man %d: this thing is like a rope", id)
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```
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The last felt its tusk, stating the thing is that which is hard, smooth and like a spear.
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```
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type Tusker interface {
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Tusk()
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}
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// in grope switch block
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case Tusker:
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log.Printf("man %d: this thing is hard, smooth and like a spear", id)
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```
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All of the men spoke fact about the thing, but none of them spoke the truth of what it was.
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```
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// after grope switch block
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log.Printf("%T", thing) // prints Elephant
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```
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---
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```
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switch thing.(type) {
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case Trunker:
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log.Printf("man %d: this thing is like a thick snake", id)
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case Fanner:
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log.Printf("man %d: this thing is like a kind of fan", id)
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case TreeTrunker:
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log.Printf("man %d: this thing is like a tree trunk", id)
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case Waller:
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log.Printf("man %d: this thing is like a wall", id)
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case Roper:
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log.Printf("man %d: this thing is like a rope", id)
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case Tusker:
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log.Printf("man %d: this thing is hard, smooth and like a spear", id)
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}
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```
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